Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as a tachycardia. The present invention is concerned with the treatment of tachycardias, which are frequently caused by the presence of an "arrhythmogenic region" or "accessory atrioventricular pathway" close to the inner surface of the chambers of a heart. The heart includes a number of normal pathways responsible for the propagation of electrical signals from the upper to the lower chambers of the heart, which are necessary for performing normal function. The presence of arrhythmogenic region or accessory pathways can bypass or short circuit the normal pathways, potentially resulting in very rapid heart contractions, referred to here as tachycardias.
Cardiac mapping is used to locate aberrant electrical pathways and currents emanating within the heart. The aberrant pathways cause heart muscle contractions to take on abnormal and life threatening dysrhythmias. Intracardiac mapping requires careful positioning of a plurality of catheters of multiple electrodes within the heart. For example, Webster, Jr. in U.S. Pat. No. 4,960,134 shows the general use of a catheter. It is important for a catheter to move into and out of the heart chamber freely without any obstruction, or potential complications of components disengaging from the catheter shaft.
Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying cause. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a clinician to be able to accurately steer the catheter to the region for ablation. Once at the region, it is important for a catheter to intimately contact the tissue site to effectively control the emission of energy to ablate the tissue within the heart.
Regardless of the type of mapping means or ablation means used, the clinician is called upon to remotely move, rotate, push, pull, and manipulate the catheters in various ways. First, a catheter is inserted into a major vein or artery, usually in the neck or groin area. It is then guided into the chambers of the heart by appropriate manipulation through the vein or artery. The distal section of a catheter must be maneuverable by a user from the proximal end of the catheter, so that the electrodes at the distal section can be positioned against the tissue at the desired location to assure that all aberrant electrical pathways are mapped and later ablated.
Development of prior catheters has focused upon the requirements of electrical continuity and interference problems. However, the mechanical and safety considerations have been overlooked. A conducting wire is soldered to the tip electrode or the band electrode. The electrode with a conducting wire is thereafter placed and secured onto the catheter shaft, mostly by adhesives. The adhering force between a tip electrode and the catheter shaft is proportional to the contact surface area. It has been reported that the tip electrode can, on occasion, disengage from the distal section of the catheter shaft. The frequency of tip electrode disengagement becomes more frequent when a longer tip electrode is used for atrial flutter applications. In an atrial flutter procedure, a tip electrode of an 8 mm length or longer is generally required. In this case, the contact area for adhesion, between the stem of the electrode and the inner surface of the catheter shaft, is not proportionally increased. The electrode is generally prone to separate from its main catheter shaft body because of inadequate contact area, and subsequently adhesive strength. If separation of the tip electrode from the catheter shaft occurred, the tip electrode could inadvertently be left behind in a patient's heart or circulation system. The prior development has overlooked the importance in providing a safe, intact catheter system having safety means, in addition to the adhesive force. It is the objective of this invention to provide the needed safety means for the electrophysiology cardiovascular catheter system having a tip electrode.